Improved performance in Cu2ZnSnSe4 solar cells using a sandwich-structured ZnSe/Cu2SnSe3/ZnSe precursor

Cu2ZnSnSe4 (CZTSe) films with different Zn/Sn ratios were fabricated using Cu2SnSe3 (CTSe) and ZnSe bilayer precursors (ZnSe/CTSe/Mo) and sandwich-structured precursors (ZnSe/CTSe/ZnSe/Mo). Using the bilayer precursor, excessive ZnSe on top of the CZTSe films with a Zn/Sn ratio of 1.3 that acts as a current-blocking barrier was observed, reducing the short-circuit current density of the CZTSe solar cells. Modification of the precursor structure from the bilayer to the sandwiched structure eliminates the segregation of ZnSe phase on top of the film even for a high (1.25) Zn/Sn ratio. This modification improved the cell efficiency from 6% (bilayer precursor) to 9% (sandwich-structured precursor).